So I also got bit by this bug that seems to be going around. I am starting to CNC convert the mill portion of a G9729 (because I already own it) and so far I have most of the process figured out. Except for the stepper motor size.

I know I want closed loop steppers. My experience in machining has been that moving the table does not require as much pressure as is required to push the tool through steel. I have seen a number of conversions that used 1200 oz/in steppers, but I don't know if that was over-design (my usual modus) or calculated.